<template>
  <div>
     <div class="box" :class="cs" @click="operClsStyle"></div>
  </div>
</template>

<script>
export default {
  data(){
    return{
      cs:''
    }
  },
  methods:{
    operClsStyle(){
    this.cs="c1"
    }   
   }
}
</script>

<style>
  .box{
    width: 100px;
    height: 100px;
    border: 1px solid #000;
    border-radius: 50%;
  }
  .c1{
    background-color: orange;
  }
</style>